Coal waste application in recycled asphalt mixtures with bitumen emulsion

Several additives are used for performance improvement of emulsified recycled mixtures such as cement and lime. This study investigated the feasibility of using coal waste and its ash in emulsified recycled mixture. Coal waste is available in huge volumes around the coal mine zones and coal washing plants that can be a serious threat to the environment. The experimental procedure of this research consisted of assessment of cold recycled mixture performance containing coal waste and its ash. Further, the environmental impact of using this waste was investigated. The results showed that utilizing coal waste and its ash improved the mechanical properties by increasing the Marshall stability, tensile strength and resilient modulus particularly in the long-term. These improvements were more obvious for coal waste ash because of its higher pozzolanic features. Coal waste ash improved resistance against moisture damages meanwhile, coal waste could not exert a positive effect on moisture sensitivity. The use of lime as a complement for coal waste and its ash resulted in development of semi-cementitious materials and increased the stiffness of recycled mixture. In addition, the findings of toxicity characteristic leaching procedure test showed that the amount of heavy metals in leachate from mixtures containing coal waste and its ash was lower than the standard level. Generally, the application of coal waste and its ash in recycled mixtures is regarded as a step toward environmental preservation by reducing the amounts of accumulated waste and the lowering of construction costs compared to other additives.